Indian budget carrier IndiGo, with a hub at New Delhi's Indira Gandhi International Airport, today firmed up an order for 250 new Airbus A320neo aircraft, allowing the country's largest airline to expand with new routes in India and South Asia.

The order is the largest in Airbus history by number, representing a potential investment of $26 billion in new aircraft by the low-cost carrier. An initial agreement was made in October, but today's announcement solidifies the deal, with the planes set to be delivered from 2018 through 2026. IndiGo is already a big customer of the airline manufacturer; a total of 530 Airbus planes have been ordered by IndiGo since 2005.

The New York Times explains the incredible growth of air travel in the region: "India is expected to become the third-largest aviation market globally by 2020, with the number of airline passengers tripling to some 450 million trips per year, as an expanding middle class trades up from slow train journeys to taking a plane."

The A320neo boasts design improvements to increase fuel efficiency—including "sharklet" wingtips, a body made partially of composite materials, and the latest in engine technology—and is proving popular with rapidly expanding low-cost airlines. AirAsia, Europe's Wizz Air, and Indonesia's Lion Air have each placed orders for another 100 aircraft, the first of which will enter service this fall.